Sizing a shower pump

[Stanios]

Yo!
Little shower pump project at hand have plenty of experience fitting them just not specifying!
I've read up on man. instructions so seems like a cheapo 2 bar salamander (price conscious customer here) is good enough for a single shower.

What threw me off was the recomendation on the instructions for a 220l tank minimum. Now my cus has 110 litre tank..eeep.. Mains is great looks like it will fill most of what it will use straight away. Pump will do about 15l/m roughly so 10 min shower should be OK I guess, as mains will fill 50 litres over 10 mins easy

Now hot water cylinder is 120litres.. I can just imagine the pump emptying it fairly quickly. At 60c it might do a 10 min shower when mixed with cold but then no hot water for next 20-30 mins.

What are my options here?
Fit the pump fingers crossed or ppsize cylinder AND tank (might as well fit unvented cyl then)?

Cheers

 

[JCplumb]

I've never been comfortable putting more than a 2 bar shower pump on gravity systems and I always tell the customers their shower times may be limited.
Last one I fitted I talked the customer down from a 3 bar to a 1.2bar shower mate pump, the results were spot on to be honest, the incoming main was about 2.5 bar and 10l/minute(if I remember correctly) so I thought the cold would just push through and drown the hot, but it didn't.

 

[Stanios]

Is fitting any shower pump on 120l hw cylinder wise?

 

[JCplumb]

Well I'm guessing you'll be using a surrey flange, so the size of the cylinder is only relevant to how long the shower stays hot, as long as the refill rate of the cylinder > the flow rate of the shower then it won't run dry. Which is why I'd go for the lowest pressure pump the customer will agree to.
You've already done a rough calculation of how long they will have hot water so give them the option of a size upgrade, put the ball in their court.

 

[Stanios]

Well I'm guessing you'll be using a surrey flange, so the size of the cylinder is only relevant to how long the shower stays hot, as long as the refill rate of the cylinder > the flow rate of the shower then it won't run dry. Which is why I'd go for the lowest pressure pump the customer will agree to.
You've already done a rough calculation of how long they will have hot water so give them the option of a size upgrade, put the ball in their court.

Thats what il do then. JC comes to aid when needed yet again. Hallelujah!

 

[Plumbstar Tom]

1.5 bar will give plenty of power for a decent shower on single use.

Just note that if that pump runs dry it will probably ruin the shaft seals and warranty will be voided if the tanks aren't to the MIs.